<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="../css/reset.css">
    <style>
        .w {
            width: 1226px;
            margin: auto;
        }

        .header {
            height: 100px;
            background-color: #eee;

            position: relative;
        }

        .header h1 {
            width: 100px;
            height: 100px;
            float: left;
            background-color: orange;
        }

        .header ul {
            width: 900px;
            float: left;
            height: 100px;
            background-color: #ddd;


            margin-left: 50px;
        }

        .header ul li {
            float: left;
            margin-left: 30px;
            line-height: 100px;


            padding: 0 10px;
        }





        .hide {
            width: 100%;
            height: 200px;
            background-color: #f00;


            position: absolute;
            left: 0;


            height: 0;
            overflow: hidden;
            transition: .3s;
        }

        .header li:hover .hide { 
            height: 200px;
        }
    </style>
</head>

<body>

    <div class="header">
        <div class="w">
            <h1>
                <a href="">mi</a>
            </h1>
            <ul>
                <li>
                    <a href="">首页</a>
                    <div class="hide">1</div>
                </li>
                <li>
                    <a href="">首页</a>
                    <div class="hide">2</div>
                </li>
                <li>
                    <a href="">首页</a>
                </li>
            </ul>
        </div>
    </div>

</body>

</html>